CC3220: GPIO, sys_config and mgos_init support

```
Using port /dev/ttyACM0
[Aug 30 19:33:02.105]
[Aug 30 19:33:02.114] cc32xx_init          c_no_libs 1.0 (20170830-163205/mos8@6587ffd6+)
[Aug 30 19:33:02.123] cc32xx_init          Mongoose OS 2017083016 (20170830-163205/mos8@6587ffd6+)
[Aug 30 19:33:02.130] cc32xx_init          RAM: 253588 total, 240044 free
[Aug 30 19:33:04.430] cc32xx_start_nwp     NWP v3.4.0.0 started, host driver v2.0.1.19
[Aug 30 19:33:04.437] mgos_vfs_dev_open    slfs_container ({"prefix": "spiffs.img.0"}) -> 20005a64
[Aug 30 19:33:04.450] cc32xx_vfs_dev_slfs_ 20005a64 spiffs.img.0.0 262144 0xfffffffffffffffe
[Aug 30 19:33:04.457] mgos_vfs_mount       Mount SPIFFS @ / (dev 20005a64, opts ) -> 20005a74
[Aug 30 19:33:06.102] mgos_vfs_mount       /: size 233681, used: 4016, free: 229665
[Aug 30 19:33:06.108] mgos_vfs_mount       Mount SLFS @ /slfs (dev 0, opts ) -> 20005ed4
[Aug 30 19:33:06.114] mgos_vfs_mount       /slfs: size 0, used: 0, free: 0
[Aug 30 19:33:06.718] mgos_sys_config_init MAC: 04A316459442
[Aug 30 19:33:06.720] mgos_sys_config_init WDT: 30 seconds
[Aug 30 19:33:06.724] Hello, world!
[Aug 30 19:33:06.728] mgos_init            Init done, RAM: 253588 total, 236544 free, 235864 min free
```

PUBLISHED_FROM=7e83c9ddcc642bd324a40e125d6636ece824fb18

mongoose.h

@@ -1226,6 +1226,7 @@ int sl_set_ssl_opts(struct mg_connection *nc);
 #define SL_ERROR_FS_NOT_SUPPORTED SL_FS_ERR_NOT_SUPPORTED
 #define SL_ERROR_FS_WRONG_FILE_NAME SL_FS_WRONG_FILE_NAME
 #define SL_ERROR_FS_INVALID_HANDLE SL_FS_ERR_INVALID_HANDLE
+#define SL_NETCFG_MAC_ADDRESS_GET SL_MAC_ADDRESS_GET
 #define SL_SOCKET_FD_ZERO SL_FD_ZERO
 #define SL_SOCKET_FD_SET SL_FD_SET
 #define SL_SOCKET_FD_ISSET SL_FD_ISSET